I would like to modify this mic. I have heard one that is complete and was quite impressed. I have very little experience with tubes and some of the component values, type and location are unclear to me. Thanks
Apex 460 Mod:
1. Remove C9 and C10 to remove the 25Khz peak resonance in the high end.
2. Change the caps in the signal path: Polystyrene input and 1uF polypropylene output (C8)
3. Change the tube to a 6072 or a very good 12AT7
4. Add a tiny EQ cap like that found in the ELA m251 design, between the Anode pin of the 1st stage tube and ground.
( I like 200pF myself but it depends on your capsule, sometimes 330pF is a better sound)
5. Change the cathode bypass cap from 100uF to 22uF to reduce low frequency rumble and distortion.
6. Change the cathode bias resistor to 1.8K to increase plate current in both tubes and improve biasing on the 2nd stage.
7. Remove the two inner layers of mesh from the headbasket
8. Add a *220K damping resistor to the output circuit across the transformer primary coil.
(after the capacitor) This resistor makes a cleaner low end by damping the remaining transformer/capacitor resonance.
Apex 460 Mod:
1. Remove C9 and C10 to remove the 25Khz peak resonance in the high end.
2. Change the caps in the signal path: Polystyrene input and 1uF polypropylene output (C8)
3. Change the tube to a 6072 or a very good 12AT7
4. Add a tiny EQ cap like that found in the ELA m251 design, between the Anode pin of the 1st stage tube and ground.
( I like 200pF myself but it depends on your capsule, sometimes 330pF is a better sound)
5. Change the cathode bypass cap from 100uF to 22uF to reduce low frequency rumble and distortion.
6. Change the cathode bias resistor to 1.8K to increase plate current in both tubes and improve biasing on the 2nd stage.
7. Remove the two inner layers of mesh from the headbasket
8. Add a *220K damping resistor to the output circuit across the transformer primary coil.
(after the capacitor) This resistor makes a cleaner low end by damping the remaining transformer/capacitor resonance.
